Lately I've often seen north koreans placed good at codeforces rounds. Looking on the ratings, I see that they have good ratings on hackerrank and codeforces. Are this profiles really from North Korea? If yes, how do they train under the existing censorship in the country?
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Some people in North Korea's universities have access to the Internet.
Did you notice that North Korea had a team in ICPC World Finals 2016?
North Korea was also one of the best teams in the International Mathematical Olympiad 2015.
How good does north Korea do in IOI and ICPC usually ?
North Korea use censorship to control information about their country and the whole world.
But if you are a member of authority and you are loyal, then you can have full access to outside world and learn more knowledge to help the authority.
So, I think most of them are loyal and they are authorized to learn from outside and help the country. And some are clever guys who can get rid of censorship.